A number of industrial processes, particularly metallurgical processes, give rise to extremely adverse environmental conditions due to the emission of heat, dirt and fumes. Provision must be made both to protect workers from these conditions, inter alia by providing an environment of clean and temperature conditioned air, and to extract the fumes produced, and there is increasing legislation setting environmental standards in this field. This presents a special problem when either the worker to be protected, or the origin of the fumes moves over an extensive path, crane operators and rail mounted fume hoods being typical examples. Further problems arise when the fumes to be extracted are at very high or even incandescent temperatures, as may occur during the emptying of coke ovens, or where high levels of heat radiation or contaminants are involved.